The present invention relates generally to a core of a magnetic head and a method of producing such a magnetic head core, and more particularly to a magnetic head core formed of ferrite with a magnetic gap, which has substantially no rear or back gap opposite to the magnetic gap and which is improved in wear resistance and cost of manufacture, and to a method of manufacturing the same.
In the art of magnetic heads for various types of recording media, a core made of ferrite has been known, which generally consists of a pair of ferrite core elements joined together to form a structure of a ring-shaped or a toric cross section having a centrally located large aperture or void which facilitates winding of coils around the core elements. More specifically, referring to FIG. 1, which shows a common type of magnetic head core, a pair of generally C-shaped ferrite core halves 2, 4 are butted together to form the core with a central aperture 6 which serves as a space for winding coils 8 around the core halves 2, 4. In this manner, an annular or toric magnetic circuit is constituted by the two C-shaped ferrite core halves 2, 4. Additionally, the toric magnetic core structure is formed with a magnetic gap 10 at one end portion of the core. The gap 10 is formed to extend across the toric magnetic circuit and has a suitable width .alpha. which is the distance between the opposed end surfaces of the core halves 2, 4. As is well known in the art, a magnetic tape 12, magnetic disk or other magnetic recording medium, is slidably moved on outer contact surfaces of the core halves 2, 4 in the proximity of the magnetic gap 10 defined by these halves 2, 4, whereby magnetic writing (recording) and reading (reproducing) processes are effected.
As indicated above, the ends of the core halves 2, 4 at one end of the core have the opposed surfaces which are spaced apart from each other by a distance equal to the width .alpha. of the magnetic gap, while the other ends of the core halves 2, 4 are bonded together with suitable bonding glass so as to maintain a generally toric cross sectional shape of the magnetic core as a whole. In this known ferrite core formed of the two core elements 2, 4 bonded together with glass, however, it is inevitable that a very small gap 14, a so called rear or back gap, is formed between the bonded abutting surfaces of the core elements 2, 4. The existence of this rear gap 14, which is located opposite to the magnetic gap 10 at the front of the core, necessarily increases the magnetic resistance of the magnetic circuit, and consequently has an adverse effect on the sensitivity, and signal to noise ratio (S/N ratio) of a magnetic head using the core, which sensitivity and S/N ratio are important characteristics of the magnetic head. In other words, it is required to completely eliminate the rear gap 14, i.e., to reduce the width of the gap to zero in order to maximize the sensitivity of the magnetic head, and accordingly improve the S/N ratio. However, this requirement has not been satisfied by any conventional ferrite core formed from a plurality core members or elements as described above.
When these core elements 2, 4 of the core are both made of ferrite polycrystal, there have been experienced troubles that the surfaces in the vicinity of the magnetic gap are subject to uneven wear due to their relative sliding contact with a magnetic recording medium such as the magnetic tape 12, and that grains of the polycrystalline ferrite drop out from opposed surfaces defining the magnetic gap, during the process of forming such gap-defining surfaces, thus causing the gap-defining surfaces to be rough having small indentations and projections. In view of these troubles, it is considered to form the core elements 2, 4 from a single crystal of ferrite. In this case, there arises another problem in addition to the presence of the aforementioned rear gap at the abutting portions of the elements. That is, extremely expensive single crystal ferrite should be used for the plurality of core elements, and the material cost of the core is accordingly increased. When relatively large ferrite core elements are required to fabricate a relatively large core, correspondingly large single crystal ferrite blocks are required, which pushes up the cost of manufacture of the core and requires a higher level of technology.